Adding initial readme.

README.md

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+# s7pp
+S7 Scheme based text preprocessor.
+
+A simple text preprocessor that's designed to process text, evaluating s-expressions prefixed with an `@` and run them via S7 and conver their output into text.
+
+## Usage
+
+`s7pp <input file> [output file]`
+
+Takes `input file` and processes it, writing output to `output file` or stdout
+
+## Examples
+
+## Expansion Rules
+
+### Prefixes
+
+S-Expressions starting with `@` will be evaluated and their results expanded in place.
+
+S-Expressions starting with `@;` will be consumed and ignored as a comment.
+
+S-Expressions starting with `@@` will be evaulated and their results discarded, useful for defining variables, functions and loading other modules.
+
+To emit a literal `@` You may prefix it like `;@` XXX, Maybe Broken!
+
+S-Expressions inside of literal double quoted strings are not expanded. XXX Reconsider?
+
+### S-Expression Expansion
+
+When expanding an S-Expression after a `@`, it can be a symbol name, in which case the value is output, otherwise an S-Expression, with matching parenthesis `(` and `)` is consumed and passed to S7 to be evaluated, and then the output is written.
+
+### Output stringification
+
+When the returned value is a literal string or character, it is simply printed directly into an output. Lists are recursively evaluated using the same rules, with non-character, non-whitespace elements interspersed with space characters, and any other s7 object is converted to a string using standard s7 string conversion rules (s7_object_to_c_string)